350 BELL SYSTEM TECHNICAL JOURNAL 



troubles return in the company of a new one. The intrinsic energy of this 

 point-particle is infinite — so says the electromagnetic theory; the mass must 

 therefore be infinite — so says the relation of Einstein of which I will presently 

 show the power. If from this alternative we rebound to that of a globule of 

 continuous electrical fluid, the old difficulties come back in the company of 

 another new one. The parts of the globule of negative electricity repel 

 each other, so our electron-model turns out to be a high-explosive bomb. 

 The reader if he wishes may seek in Lorentz' "Theory of Electrons", a classic 

 of some thirty years ago, the details of a scheme for preventing the electron 

 from exploding by means of nonelectrical forces — a surrender, therefore, of 

 the viewpoint that the ultimate forces are electrical. 



Leaving these difficulties still unmastered, I turn to nuclear physics. This 

 is a term which covers two fields: on the one hand, the structure and the 

 qualities of atom-nuclei; on the other, some remarkable attributes of 

 electrons, which they display either when they have tremendous energies, 

 or under conditions which it takes tremendous energies to create. "Tre- 

 mendous" energies are enjoyed by electrons fresh from radioactive sub- 

 stances, are obtained from the cyclotron and the electrostatic generator, 

 and are found at their extremest in the cosmic rays. Of these attributes 

 the only one which I will mention is mortality. 



Mortality: this is a very obnoxious attribute for an elementary particle. 

 All atomists heretofore have devised their atoms specifically to be immortal, 

 to be the immortal things, to be the one thing permanently changeless under 

 the flux of phenomena. But the electron is mortal, subject to birth and to 

 death. Electrons are born in pairs, a positive and a negative springing to- 

 gether into existence. Electrons die in pairs, a positive uniting with a 

 negative and the two of them passing out of existence. 



These are not exactly cases of something coming out of nothing and 

 something turning into nothing. Energy, mass and momentum are all 

 conserved. Corpuscles of light disappear where and when an electron-pair 

 is born, are born where and when a pair of electrons vanishes. So far as 

 can be told, the corpuscles of light possess just the energy, just the mass 

 and just the momentum which is destined to go to the nascent electrons or 

 to be left unpossessed by those about to die. Now I have to admit my 

 fault in not elevating earlier the corpuscles of light to a parity with the 

 electrons and the atoms. They have the singular attribute of moving 

 always with the same speed (when in a vacuum); they do not collide with 

 one another, or rather such collisions have not been detected, though 

 collisions with electrons are known; and they suffer from mortality, very 

 much more so than do electrons. (Positive electrons are so rare, that 

 negative electrons enjoy an almost perfect security.) Immortality is re- 

 served for energy and mass and momentum. Now we feel ourselves swerv- 



